Additive manufacturability of superalloys: Process-induced porosity, cooling rate and metal vapour

Digital technology such as metal additive manufacturing (AM) provides flexible process design freedom to fabricate intricate three-dimensional structures layer-by-layer. However, its manufacturability relies on the fundamental understanding of melt pool physics and fluid (metal) dynamics. The effect of metal vapour and porosity induced during the laser-materials interaction can influence the additive manufacturability. In this work, composition-process relationship of laser-based powder-bed fusion (L-PBF) AM is studied via computational fluid dynamics modelling to rationalise solid-liquid-vapour transformation where empirical-based approach is used to generate thermo-physical property of about 100 nickel-based superalloys at the liquid state. It is found that with larger vapor mass loss, the porosity tends to be higher. However, the higher vapour mass loss means faster cooling rate. This is indicated that the thermal-fluid flow process, which is also governed by the thermo-physical property, strongly affects the additive manufacturability. Additive manufacturability map based upon porosity, cooling rate from liquid to solid, volatile mass loss criteria has been established to link the composition in nickel-based superalloys with their thermo-physical property. This offers a thermal-fluid science based tool in designing compositions of novel superalloys for AM applications.